The invention relates to a device for producing sponge iron.
1. Field of the Invention
Lumps of iron oxide are reduced in a reduction shaft with a dust-containing and carbon monoxide-rich reduction gas from a fusion gasifier in an iron ore reduction melting plant. In this situation, only a part of the void volume of bulk material in the reduction shaft can be used to receive the dust which is introduced with the reduction gas into the reduction shaft. With plants in which the reduction shaft is connected to the fusion gasifier through downpipes, an additional amount of dust, beyond that introduced with the reduction gas, is introduced with the gasifier gas through the downpipes and discharge devices into the lower area of the reduction shaft. The dust content of this gasifier gas is several times higher than that of the reduction gas being purposefully introduced into the reduction shaft which has been previously dedusted within hot gas type cyclones. In addition to this dust, dust by virtue of the air separation of the discharged sponge iron and in case of the calcined aggregates is additionally conveyed back to the reduction shaft by the flow up of the gasifying gas. The total dust results in an increased dusting of the lower area of the reduction shaft, in channeling, hanging of the bulk material as well as in an uncontrolled discharge of the sponge iron by the discharge devices. A particularly disadvantageous effect is in that the dust passing via the downpipes from the fusion gasifier into the reduction shaft includes tar-containing and coal particles which are only partially degasified as well as other components which result in nodulizing.
With a more intensive dusting of the iron oxide bulk material in the bustle and inlet areas of the reduction gas, respectively, the pressure difference between the fusion gasifier and the lower area of the reduction shaft is increased and, accordingly, the highly dusted gasifying gas flowing up via the downpipes and screw type extractors, through which such has a direct access to the low dusted bulk material in the center of the reduction shaft. By this increased pressure difference the air separation is increased in the downpipes. Therefore, the content of dust becomes higher and higher and the bulk material in the lower area of the reduction shaft can be enriched with the circulation dust. Because of the high frictional forces within the bulk material enriched with dust, quite low pressure differences are sufficient to cause hanging of the bulk material which results in the well known phenomena of channeling and the undisturbed gas flow comprising a very high dust content from the fusion gasifier into the reduction shaft. A part of the dust is further conveyed from the lower area of the reduction shaft upwardly into the reduction zone and leads to dusting the bulk material and channeling therein as well. Such intensive dustings of the bustle area can occur if too much undersize powder is introduced with the coal by employing a greater quantity of coal in the coal mixture which highly disintegrates at high temperatures when extremely increased temperatures appear in the gasifier which result in a greater disintegration of the coal with a more intensive disintegration of the ore in the reduction shaft and with a failure and partial failure of the dust recirculation, respectively. When such cases occur the reduction shaft requires a rather long time until it cleans the dust since a part of the dust is again and again conveyed upwardly through the formed channels.
A part of the remaining void volume is filled up by the fine particles which are introduced with the raw material and which partly originate in the reduction shaft by the reduction of iron carriers and the calcination of aggregates, respectively. With this, the capacity of the reduction shaft is highly limited since a greater part of the void volume has to be maintained for the flow of the reduction gas through the bulk material, hence the specific quantity of the reduction gas required at minimum for the reduction of iron oxides and calcination of aggregates can be led through the reduction shaft having a moderate and upwardly limited pressure drop. Upon exceeding a particular pressure drop, which pressure drop depends on the particle size, particle composition and void volume of the bulk material, such well known xe2x80x9changingxe2x80x9d of the bulk material occurs as well as such channeling and cross-flow of a part of the reduction gas through the channels without being participated with the reduction process. Based on the above, the result is a low degree of metallization, low carburization of the sponge iron, a low degree of calcination of the aggregates, low plant performance as well as a poor quality of the crude iron. Hence, for normal operation a minimum specific quantity of the reduction gas is required which is led through the reduction shaft without channeling and without hanging of the bulk material. This specific required quantity of reduction gas depends on the degree of oxidation of the reduction gas, the iron content of the iron oxides, disintegrating features of the employed iron oxides at low temperatures, the quantity and disintegration features of the aggregates as well as other factors and is about 1050 mn3 reduction gas per ton of iron oxides. Because of the high temperatures of the gasifying gas and because of a low pressure drop within the bulk material serving as gas blocking means for the gasifying gas not being dedusted via the downpipes, the pressure drop is determined by a large cross section of the reduction shaft in the lower area, brick lined hot gas type cyclones having a moderate efficiency are employed as dedusting units for the reduction gas such that this still additionally contains considerable quantities of dust as well and thereby with the specific quantity of reduction gas a relatively low tolerance towards the top is given. By introduction of the reduction gas in the bustle area only at the circumference of the reduction shaft, the portion of void volume of the bulk material still being freely available for the dust separation in the radial center of the reduction shaft is hardly used. Therefore the specific quantity of reduction gas which can be led through becomes still smaller and the external ring of the bulk material within the portion of the gas inlets is more highly dusted than necessary. Then, in this external ring, channeling and hanging commence. The greater the diameter of the reduction shaft, the smaller the specific quantity of reduction gas which can be led through the reduction shaft without hanging and without channeling.
2. Description of the Prior Art
From JP-A-62294127 is previously known a device for producing sponge iron from iron oxides in a reduction shaft by using a reduction gas. This reduction gas is introduced into the reduction shaft through several gas inlets arranged at the same height around the circumference of a reduction shaft. Additionally, below the plane of these lateral gas inlets another gas inlet for the reduction gas is provided in the radial center of the reduction shaft. This gas inlet is formed by the inner open end of a pipe radially extending from the outside toward the center of the reduction shaft, with the pipe being closed in its longitudinal direction and reduction gas is supplied via the external open end thereof. By this measure a more uniform reduction of iron oxides over the shaft cross section is to be obtained. Problems involved with the introduction of a dust-containing reduction gas are not explained herein.
Moreover, U.S. Pat. No. 4,118,017 discloses a device for producing sponge iron from iron oxides in a reduction shaft by using a hot reduction gas which is supplied approximately in the central height of the reduction shaft through several gas inlets disposed around the circumference thereof. The reduction shaft tapers at the lower end wherein this end comprises several inserted truncated sections. At the outer circumference of each of these sections gas inlets for a cold reduction gas used as cooling gas for the sponge iron are located. Herein problems involved with the employment of a dust-containing reduction gas are not considered as well.
Hence, it is the object of the present invention to improve a generic device in that a carburization and enlarged reduction of the sponge iron are obtained, the low dusted bulk material in the radially central area is used for the dust separation, a greater pressure drop occurs within the bulk material in the lower area of the reduction shaft such that hot gas type cyclones having a greater pressure drop and hence a higher degree of separation can be employed for dedusting the gasifying gas used as reduction gas, the quantity of the dust-containing gasifying gas flowing via the downpipes into the reduction shaft is highly limited, and by means of a uniform dusting of the whole bulk material no additional pressure difference occurs via the pipe connections and downpipes, respectively, between the fusion gasifier and the lower part of the reduction shaft.
This object is solved according to the invention by using a hot, dust-containing and carbon monoxide-rich reduction gas, comprising a gas generator wherein the reduction gas is generated by partial oxidation of solid carbon-containing materials and a reduction shaft to which the reduction gas is supplied through several lateral reduction gas inlets which are arranged at the same height around the circumference of said reduction shaft at the lower end of the reduction zone, and the lumps of iron oxide are introduced into the reduction shaft, through a top area of the reduction shaft and discharged as sponge iron at a bottom end of the reduction shaft, characterized in that additional reduction gas inlets, at least one of said additional reduction gas inlets forming a downwardly open channel which extends from the outside into a radially central area of the reduction shaft are arranged below the plane of the lateral reduction gas inlets. Advantageous improvements of the device according to the invention result from the dependent claims.